The Somerset herald. [volume] (Somerset, Pa.) 1870-1936, 1887-08-24
THE LOGIC OF THE TIDES.
Rising Fifty Feet in the Bay of
Fundy and Five Feet at
New York.

New York.
A correspondent who signs his letter
with the initials D.. B. g., asks the New
York SRA number Of questions about
the interesting subject Of the tides.
Among other things be wants io know
what causes the tides. and whether IL
daI wave enters the eastern end Of Long
Island Sound aud another at the Narrows
at the same time, and. # 50, where the
two waves meet He has noticed that
on a certain date high tide at Sandy
Hook occurred in the afternoon twenty
three minutes more than twelve hours
after il occurred IN the forenoon, while at
Hell Gate the evening tide was twelve
hours and tbirty-four minutes afier the
morning one, showing that the tide was
rated eleven minutes more at Hell Gate
than at Sandy Hook. He wants to know
why this was 50. He has heard that the
difference between high and low water
at St. John, n b., or that the rise of the
tide al that place is thirty feet, while in
New York it is only from four to five
feet, and he wants to know why that is
30.
The rise and fall Of the the tide, that
is. the elevation and depression Of the
surface Of the water ofthe ocean and the
bays and tributaries that empty into il,
are due in general TO the attraction Of
the sun and moon on the earth. The sur
face of the earth that is nearest TO the
sun and moon, when the two are in line
on one side of the earth, is attracted
more strongly toward those bodies than
the centre Of the earth is, because
the surface is nearer 10 them than the
centre is; the centre is attacted toward
them more strongly than the further sur
face Of the earth is Tor the same reason.
These great heavenly bodies are constant
ly pulling the earth toward them, and
the particles OF water in the sea on the
side nearest are affected so much by this
influence that they are heaped up as if
endeayoring to fy of toward the power
that is Pulling them. But the centre Of
the earth being attracted more strongly
than the further surface, the water on
the further surface is heaped up because
the earth falls away from il as ii drops
from the straight line Of tangent through
the curve that it follows. The water on
the further side Of the earth comes drag
ging on behind, much as a whip-lash fol-
lows the Ship-stalk that il waved through
the air, while the water on the near side
OF the earth j. heaped up as iron Filings
heap up on a table when placed beneath
a powerful magnet. Thus il happens
that We have two tides in day. One is
the heap Of water drawn up by the direct
attraction of the sun and moon on il
the other that follows little over twelve
hours later is the heap or wave that is
piled up because the earth drops away
from it,
1t regularly happens every month that
the moon is on one side of the earth pull
ing the water IN its direction, while the
sun is on the opposite side pulling the
water toward it, instead of both being on
one side. The effect of this is much the
same on the water rs when both are ON
one side. 1t is on such dates as these
namely, when there has been a new
moon and when there has been full
moon-that the tides rise highest the
moon and the sun both work together
then in heaping up the water. Bu, at
the first and third quarters of the moon
the sun and the moon work against each
other. The heap Of water that the sun
ispulling along after it as il apparently
travels around the earth comes into port
just as the moon is trying TO drain it,
location one-half the way around to the
opposite side Of the earth. The conse-
quences is that the suns heap of water
partly fills up the depression caused by
the moon. Where the the moon is heap
ing up the water the sun is drawing il
away, and the consequences is that the
tide levels are neither 80 high 50 low
at such times in the months as they are
when the two great lnminaries work to-
gether. The high tides of the new and
the fail of the moon are known of as
spring tides; the low tides Of the first
and third quarters are called heap tides.
The moon, II IL observed, always gets the
best OF the sun when the two are not
working together This is due to the
nearness Of the moon 10 the earth. Al
though the sun is many times larger than
The moon, the moon eXerts more than
twice as much power on the water. But
this power is modified in various ways.
The sun may be on one side Of the equa-
tor and the moon on the ether side of
the equator and the earth. They would
not then pull together quite as well as
when both were on one side of the equa-
tor and in a right line. The earth NAV
he very near 10 the sun. as il is in Janu-
AIRY, which would increase the relative
influence Of the sun or it may be
iar away, as il Is now, when the moon is
relatively more powerful Then the moon
varies in IFS distance from the earth, too.
and tins tends TO complicate matters.
Then there are influences local to var
ious parts of the earth that vary the rise
and fail OF the tides Thus, if for cou-
pie OF days or so when the spring tides
are on us, there should prevail strong
southeast wind, the water in New York
would be heaped up 50 that ferry passen-
gers would feel as if they were climbing
stairway when they went up the bridges
10 the boats, while all the rats along
South and West streets would get drown
ed ont.
New York itself is pretty well situated
for high tide, hut not 50 well as Boston.
and not nearly 50 well as -. John. \. b.
although the rise of the tide at II. John
is but nineteen feet instead of thirty. as
the correspondent had beed told. Ifanv
one viii look at a map of North Amer
ica he viii see that iron Florida to Cape
Hatteras the land sweeps in forming a
very long, shallow bay, with Savannah
about at the head Of the bay. North Of
this there IL another bay, of which Hat
teras may be called one headland and
Nantucket Island another. New York is
in the blight, or at the lower end of Flor
ida rises less than two feet brt n, Savap.